Valve vented redundant stem seal system

ABSTRACT

A valve includes a stem seal assembly that prevent fluid flow in a first direction and vents in a second direction opposite the first direction. The assembly includes a packing assembly positioned within a valve stem opening of a valve body of the valve to seal a valve stem to the valve body. The packing assembly includes a first seal and a second seal preventing passage of fluid from a body cavity of the valve body to an exterior of the valve body along the valve stem while venting fluid from an exterior of the valve body to the body cavity along the valve stem. The packing assembly isolates the first seal and the second seal so that a load applied to the first seal ring is not transferred to the second seal ring.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to valve stem seals and, inparticular, to a valve vented redundant stem seal system.

2. Brief Description of Related Art

A gate valve has a body with a central chamber that is intersected by aflow passage. A gate moves within the chamber between the open andclosed positions. The gate has a hole through it that aligns with theflow passage while in the open position. The gate may be of a splittype, comprising two halves or it may comprise a single slab. A stemextends into engagement with the gate for moving the gate between openand closed positions. The chamber has a central portion, which isintersected by the flow passages, and a stem portion that extends fromthe central portion.

In one type, the stem extends into rotatable engagement with a threadednut or sleeve secured to the gate. Rotating the stem causes the gate tomove linearly. In another type, the stem does not rotate. A threaded nutsleeve mounted in the bonnet of the valve engages the stem, and whenrotated, causes the stem to move linearly. The threads of the sleevesand stem may slide against each other, or they may employ balls betweenthe grooves for reducing friction.

Gate valves may be operated manually, such as with a wheel mounted tothe stem or the nut sleeve. It is also known to utilize a remoteoperated vehicle (ROV) to engage and rotate a stem or nut sleeve.Hydraulically powered actuators are also utilized wherein a piston movesthe stem linearly without rotation. Electrical actuators are also knownthat employ an electrical motor and a gear train to rotate a stem or nutsleeve to cause movement of the gate.

Typically, a seal in the stem portion of the chamber engages the stem toseal pressure within the chamber. The pressure exerted on the stem sealcan be quite great, leading the stem seal to fail. When the stem sealfails it will allow fluid or gas to flow out of the valve around thestem. Some prior art embodiments provide a second seal that will sealthe valve stem to the valve body in the event the primary seal fails.This provides redundancy within the valve stem seals that increases thereliability of the seals.

Where a second seal is used, in the event the first seal leaks, a volumeof fluid will be held between the failed first seal and the second seal.Depending on the size of the spacing between the first seal and thesecond seal, the volume can be quite small. The small volume size allowsfluid pressure within the volume to rapidly reach the internal systempressure. This is not a rare condition as many of the environments inwhich the valves are placed are subject to extreme pressure loads formany years, greatly increasing the likelihood that the primary seal willleak or fail. When the valve is opened, pressure may then quickly ventout past the leaking seal. This can cause further damage to the primaryseal so that what had been a small leak becomes a larger failure of theprimary seal. A larger failure of the primary seal may eliminate anybenefit the leaking primary seal provided, increasing the likelihood ofsubsequent secondary seal failure. Thus, there is a need for a stem sealwith high reliability brought by redundant seals, while allowing for theseals to vent in instances of leakage past the primary seal.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention that provide a valve vented redundant stem sealsystem, and a method for using the same.

In accordance with an embodiment of the present invention, a valvehaving a stem seal assembly is disclosed. The valve includes a valvebody defining a flow passage and a body cavity perpendicular to the flowpassage. The valve body defines a stem opening extending from anexterior of the body into the body cavity. The valve includes a valvemember moveable between an open position and a closed position, thevalve member having a hole therethrough which registers with the flowpassage when the valve member is in the open position. The valve alsoincludes a valve stem having a valve stem axis coupled to the valvemember, the valve stem extending from the body cavity to an exterior ofthe valve body through the valve stem opening for moving the valvemember from the closed position to the open position. A packing assemblyis positioned within the valve stem opening to seal the valve stem tothe valve body. The packing assembly includes a seal ring having achevron profile defining a first and a second leg extending from an apexof the chevron radially outward, the first and second legs for sealingto opposing annular surfaces. The packing assembly includes a back ringhaving a chevron channel so that an apex of the seal ring may insertinto the channel, the back ring having a greater stiffness to radialmovement than the first and second legs to limit radial deformation ofthe first and second legs.

In accordance with another embodiment of the present invention, a gatevalve stem packing assembly for sealing a gate valve stem to a gatevalve body having a body cavity is disclosed. The packing assemblyincludes a packing ring situated within the stem opening so that anouter diameter of the packing ring abuts the inner diameter of the stemopening, and an inner diameter of the packing ring abuts an outerdiameter of the valve stem. The packing ring defines a first annularrecess on the outer diameter of the packing ring and a second annularrecess on the inner diameter of the packing ring. The assembly alsoincludes a packer retainer ring positioned coaxial with the packing ringand secured to the valve body so that the packer retainer ring securesthe packing ring to the valve body. The packer retainer ring defines athird annular recess on the outer diameter of the packer retainer ringcoaxial with and axially above the first annular recess. The packingring defines a fourth annular recess proximate to the packer retainerring, the fourth annular recess coaxial with and axially above thesecond annular recess. A seal is positioned in each annular recess sothat each seal prevents passage of fluid in a first direction and ventsfluid in a second direction opposite the first direction.

In accordance with yet another embodiment of the present invention, aseal ring for a gate valve is disclosed. The seal ring includes anannular seal stand off having a first end and a second end. The sealring also includes a seal ring having a chevron profile positioned onthe seal standoff so that the second end of the seal stand off insertsinto the chevron profile. The seal ring defines a first and a second legextending from an apex of the chevron radially outward, the first andsecond legs for sealing to opposing annular surfaces. An energizingspring having a chevron profile is interposed between the seal stand offand the seal ring, the energizing spring exerting an expanding force onlegs of the seal ring so that the seal ring will remain in sealingcontact with the opposing annular surfaces. The energizing spring may bedeflected in response to a fluid pressure on the seal ring opposite theenergizing spring to allow fluid flow past the seal ring. The seal ringincludes a back ring having a chevron channel so that an apex of theseal ring may insert into the channel, the back ring having a greaterstiffness to radial movement than the first and second legs of the sealring to limit radial deformation of the first and second legs of theseal ring. The first end of the seal stand off has a substantially flatportion positioned on a supportive shoulder of the packing assembly andthe second end of the seal stand off is in operative engagement with thechevron profile. The seal ring is formed of a polymer and the back ringis formed of a polymer having a greater hardness than the polymer of theseal ring. The channel of the back ring extends only partially to distalends of each leg of the seal ring. A width of the back ring is smallerthan the distance between the seal ring legs, and the back ring does notsealing engage the stem. The channel of the back ring extends from theapex of the seal ring over only part of the seal ring.

An advantage of a preferred embodiment is that it provides trueredundant sealing while still allowing for pressure relief venting whenneeded. Thus, any leakage past the primary seal does not cause damageto, or further failure of, the primary seal when fluid vents past theprimary seal when the valve is opened. Still further, the seals operateindependently to reduce the wear on the seal assembly and prolong thelife of the seal assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features, advantages and objects of theinvention, as well as others which will become apparent, are attained,and can be understood in more detail, more particular description of theinvention briefly summarized above may be had by reference to theembodiments thereof which are illustrated in the appended drawings thatform a part of this specification. It is to be noted, however, that thedrawings illustrate only a preferred embodiment of the invention and aretherefore not to be considered limiting of its scope as the inventionmay admit to other equally effective embodiments.

FIG. 1 is a partial sectional view of a gate valve in accordance with anembodiment of the present invention.

FIG. 2 is a detail view of a portion of the gate valve stem as indicatedon FIG. 1 in accordance with an embodiment of the present invention.

FIG. 3 is a detail view of a gate valve stem seal as indicated on FIG. 2in accordance with an embodiment of the present invention.

FIG. 4 is a top view of a back ring of the gate valve stem seal of FIG.3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more fully hereinafter withreference to the accompanying drawings which illustrate embodiments ofthe invention. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theillustrated embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout, and the prime notation,if used, indicates similar elements in alternative embodiments.

In the following discussion, numerous specific details are set forth toprovide a thorough understanding of the present invention. However, itwill be obvious to those skilled in the art that the present inventionmay be practiced without such specific details. Additionally, for themost part, details concerning valve construction, uses, and the likehave been omitted inasmuch as such details are not considered necessaryto obtain a complete understanding of the present invention, and areconsidered to be within the skills of persons skilled in the relevantart.

Referring to FIG. 1, gate valve 11 has a body 13 and a flow passage 15that extends transversely through body 13. Valve 11 has a gate 17 with ahole 19 therethrough. Gate 17 can be designed in one piece or twopieces. Gate 17 may be split into two slabs; each slab of gate 17 musteither be open or closed at the same time. Gate 17 is shown in theclosed position in FIG. 1. Valve 11 shown in FIG. 1 is a rising-stemtype valve; however, this invention can similarly be used onnon-rising-stem type valves. When gate 17 is in the open position, hole19 of gate 17 registers with flow passage 15 of body 13 thereby allowingflow through valve 11. When gate 17 is closed as shown, hole 19 nolonger registers with flow passage 15, blocking flow of fluid throughpassage 15 and valve 11. Flow passage 15 intersects a central cavity orchamber 21 located in body 13. A counterbore is formed in flow passage15 at each intersection with chamber 21. A seat ring 27 locates in eachcounterbore to seal flow passage 15 to gate 17 while gate 17 is in theclosed position. Gate valve 11 also includes a stem 29 coupled to gate17. Stem 29 has an axis 25 passing through a center of stem 29. Stem 29is linearly moveable without rotation along axis 25 to actuate gate 17between the open and closed positions. In the illustrated embodiment, abiasing assembly 31 couples to body 13 around stem 29 to bias stem 29and gate 17 to the closed position. As illustrated, valve 11 ishydraulically actuated. A remotely operated vehicle may interface withbiasing assembly 31 to move stem 29 and gate 17 from the closed positionshown, to an open position wherein hole 19 registers with flow passage15. A packing assembly 33 provides sealing for stem 29 where stem 29passes through body 13. A person skilled in the art will understand thatgate valve 11 is an exemplary valve. The disclosed embodimentscontemplate and include any valve having a stem passing through a valvebody to operate a valve member located within the body.

Referring to FIG. 2, packing assembly 33 is shown in more detail.Packing assembly 33 includes at least one seal 35, four of which areshown in FIG. 2: a first seal 35A; a second seal 35B; a third seal 35C;and a fourth seal 35D. As shown in FIG. 3, each seal 35 includes a standoff 37, an energizing spring 39, a seal ring 41, and a back ring 43.Seal stand off 37 comprises an annular ring or protrusion having a firstend 45 and a second end 47. First end 45 of seal stand off 37 has asubstantially flat portion 49 so that seal stand off 37 may bepositioned on a supportive cylindrical shoulder within packing assembly33. Second end 47 of seal stand off 37 is opposite first end 45 andcomprises a protrusion in contact with energizing spring 39 to properlyposition seal ring 41 against back ring 43 and limit undesired axialcompression of seal ring 41. Seal stand off 37 will provide a supportfor seal 35, preventing excessive compression of seal 35 by reacting toforces directed from second end 47 toward first end 45. Seal stand off37 will be formed of a material having sufficient resistance tocompression so that seal stand off 37 will not collapse duringoperational use of seal 35.

Seal ring 41 comprises an inverted V-shaped , chevron shaped member, orchevron profile so that an apex 51 of the V-shape and the second end 47of seal stand off 37 face in the same direction. Seal ring 41 alsoincludes a first leg 53 and a second leg 55. First leg 53 and second leg55 extend toward first end 45 of seal stand off 37. In addition, a widthbetween distal ends 57, 59 of first leg 53 and second leg 55,respectively, is greater than the width between first and second legs53, 55 of seal ring 41 at apex 51. Thus, seal ring 41 is wider proximateto first end 45 of seal stand off 37 than at apex 51. In the exampleshown, the exterior surfaces of legs 53, 55 incline at a first angle αfrom apex 51 to a junction 52. Legs 53, 55 incline at a second angle βfrom junction 52 to distal ends 57, 59. Junction 52 is spaced closer toapex 51 than to distal ends 57, 59. Angle β is smaller than angle αrelative to an axis 54 bisecting legs 53, 55 and passing through apex51. When energized, distal ends 57, 59 may contact at least one of stem29 (FIG. 2) and body 13. Seal ring 41 has an interior surface 42 facingseal stand off 37 and an exterior surface 44 facing back ring 43. Sealring 41 may be formed of a fluorocarbon material such as Teflon. Aperson skilled in the art will understand that other materials havingsimilar properties to the fluorocarbon material disclosed herein arecontemplated and included in the disclosed embodiments.

Energizing spring 39 is an annular spring interposed between seal ring41 and seal stand off 37. Energizing spring 39 has a V-shapedcross-sectional profile similar to that of seal ring 41 so that asurface of energizing spring 39 may contact interior surface 42 of sealring 41. An apex 61 of energizing spring 39 will face in the samedirection as second end 47 of seal stand off 37 and apex 51 of seal ring41. Energizing spring 39 includes a first leg 63 and a second leg 65that run parallel to and generally in contact with first leg 53 andsecond leg 55, respectively. Energizing spring 39 has a spring constantsuch that energizing spring 39 will resist compression of first leg 63and second leg 65 toward seal stand off 37 during normal operatingconditions. Preferably, when seal 35 is placed within packing assembly33, seal ring 41 and energizing spring 39 will undergo a slightdisplacement toward each other of first legs 53, 63 and second legs 55,65 of seal ring 41 and energizing spring 39, respectively. Thisdisplacement causes energizing spring 39 to exert a reactive forceagainst compression of energizing spring 39, and thus compression ofseal ring 41, toward seal stand off 37. As a result, when placed withinpacking assembly 33, energizing spring 39 will cause first and secondlegs 53, 55 of seal ring 41 to seal to at least one of stem 29 and body13. In the illustrated embodiment, energizing spring 39 is formed of acobalt-chromium-nickel alloy such as ELGILOY®. A person skilled in theart will understand that other materials having similar properties tothe cobalt-chromium-nickel alloy disclosed herein are contemplated andincluded in the disclosed embodiments.

Back ring 43 may be an annular ring positioned adjacent seal ring 41opposite energizing ring 39 and seal stand off 37. Back ring 43 has agenerally square shaped cross sectional profile. Preferably, back ring43 defines a channel 67 adjacent to seal ring 41. Channel 67 may have aV-shaped profile matching the profile of exterior surface 44 formed byseal ring 41 so that channel 67 may abut apex 51 and a portion ofexterior surface 44 of seal ring 41. Channel 67 may extend at least partway along exterior surface 44 of first and second legs 53, 55 of sealring 41. In the embodiment shown, back ring 43 extends along legs 53, 55less than half of the length of legs 53, 55 from ends 57, 59 to apex 51.The tips of back ring 43 are approximate with junction 52. Back ring 43may have a width less than the width at distal ends 57, 59 of first andsecond legs 53, 55, respectively, of seal ring 41. Thus, back ring 43preferably does not seal to either stem 29 or body 13. Back ring 43 mayalso have a substantially flat surface 69 opposite surface 49 of firstend 45 of seal stand off 37. Surface 69 may be positioned proximate toan oppositely facing shoulder 56 within packing assembly 33 so thatsurface 69 may land on the shoulder 56 during operational use of seal35. In the illustrated embodiment, back ring 43 may be formed of apolyether ether ketone (PEEK) material of sufficient strength to resistyielding or deformation during operational uses that may compress backring 43 between seal ring 41 and shoulder 56 of packing assembly 33.Preferably, back ring 43 has hardness greater than the hardness of sealring 41. A person skilled in the art will understand that othermaterials having similar properties to the PEEK thermoplastic disclosedherein are contemplated and included in the disclosed embodiments. In anembodiment, back ring 43 bonds to seal ring 41. In another embodiment,back ring 43 does not bond to seal ring 41.

Back ring 43 also includes a plurality of bumps 60 formed on one or bothof the inner diameter surface and the outer diameter surface of backring 43. For example, second seal 35B of FIG. 2 includes bumps 60 formedon the outer diameter of back ring 43 proximate to packing ring 71 asshown in FIG. 3. In other seal 35 placements, bumps 60 may be formed onthe inner diameter of back ring 43. Bumps 60 may be formed of the samematerial as back ring 43 and integral with back ring 43. Each bump 60has a generally trapezoidal shaped cross sectional profile, and extendsa fractional portion of the circumference of the back ring 43 as shownin FIG. 4. Each bump 60 forms a channel 62 with an adjacent bump 60.Fluid under a higher pressure proximate to surface 69 of back ring 43vents through channels 62 to flow to an area of lower pressure proximateto interior surface 42 of seal ring 41. Thus, bumps 60 extend the usefullife of seal 45 by preventing catastrophic failure of seal 35 due to abuildup of pressure in the non-sealing direction.

In an operation, seal 35 will perform both sealing and ventingfunctions. As shown in FIG. 3, seal 35 provides a sealing function inresponse to fluid or gas pressure on interior surface 42 of seal ring41. As gas or fluid pressure attempts to move from interior surface 42to exterior surface 44 in FIG. 3, a seal initially energized byenergizing spring 39 will prevent passage of fluid or gas past distalends 57, 59 of seal ring 41. Increasing fluid or gas pressure will exerta force on energizing spring 39 and interior surface 42 of seal ring 41,pushing distal ends 57, 59 and first and second legs 53, 55 of seal ring41 into tighter sealing contact with the surfaces to which seal ring 41is sealed. Thus, as pressure increases on interior surface 42, the sealforce of seal ring 41 will increase.

As fluid pressure increases on interior surface 42 of seal ring 41,pushing distal ends 57, 59 into tighter sealing contact with adjacentsurfaces, back ring 43 will exert a reactive force on exterior surface44 through channel 67. The portions of legs 53, 55 from junction 52 todistal ends 57, 59 are not directly restrained from flexing outward byback ring 43. Increased fluid pressure applied to interior surface 42may cause first and second legs, 53, 55 to collapse against adjacentsurfaces, or in extreme cases, force portions of first and second legs53, 55 to extrude between sides of back ring 43 and adjacent surfaces ofpacking assembly 33 and at least one of stem 29 and body 13. Tocounteract this, channel 67 will exert a reactive force to compressionof seal ring 41 against back ring 43 caused by increased fluid pressureon interior surface 42. The matching profile of channel 67 and exteriorsurface 44 will allow channel 67 to resist permanent deformation of sealring 41. By preventing or limiting permanent deformation of seal ring 41in situations where high pressure is exerted on interior surface 42,back ring 43 aids in prolonging the operational life of seal ring 41 andthus seal 35.

As shown in FIG. 3, seal 35 provides a venting function to fluid or gaspressure on exterior surface 44 of seal 41. In the event that fluid orgas leaks around seal ring 41 during prolonged use of valve 11, fluid orgas may become trapped in a volume adjacent exterior surface 44. Thefluid may be trapped in a volume between second seal 35B and fourth seal35D. Alternatively, the fluid may be trapped in a volume of between thesecond seal 35B and load ring assembly 99. Continued operation of valve11 may quickly raise the pressure of the trapped volume of fluid onexterior surface 44 to that of the pressure on interior surface 42 ofseal ring 41. When gate 17 moves to the open position, allowing fluidflow through flow passage 15 of valve 11, a pressure differential arisesbetween exterior surface 44 and interior surface 42 of seal ring 41,such that a higher pressure exists on the side of exterior surface 44.The narrower width of back ring 43 relative to the width of seal ring 41and channels 62 formed by bumps 60 will allow the trapped fluid to flowpast back ring 43. Bumps 60 maintain a separation between the innerdiameter of packing ring 71 at annular recess 87 and back ring 43,providing a flow path for the trapped volume of fluid that allows forventing of the fluid under suitable situational conditions. The fluidpressure may then exert a force on exterior surface 44 of seal ring 41overcoming the spring force of energizing spring 39. The higher pressureon exterior surface 44 may compress first and second legs 53, 55 of sealring 41 to seal stand off 37, removing distal ends 57, 59 from sealingcontact with the adjacent surfaces. The trapped fluid or gas may thenflow past seal ring 41 to the low pressure side of interior surface 42.

Once sufficient pressure has vented past seal ring 41, the spring forceof energizing spring 39 will overcome the force exerted on exteriorsurface 44 by the fluid, or gas pressure and move distal ends 57, 59 offirst and second legs 53, 55, respectively, back into sealing contactwith the adjacent surfaces. Seal stand off 37 positions seal ring 41 asufficient distance from the supporting shoulder in contact with flatportion 49, allowing this displacement of seal ring 41. In addition,seal stand off 41 prevents axial movement of seal ring 41 during thispressure venting operation. Thus, seal 35 provides a seal to highpressure forces exerted against interior surface 42 of seal ring 41 anda vent to high pressure forces exerted against exterior surface 44 ofseal ring 41. Following venting, energizing ring 39 may return seal ring41 to the energized position, preventing flow from interior surface 42to exterior surface 44 when valve 11 is closed.

As shown in FIG. 2, packing assembly 33 includes four seals 35 in thisexample. Packing assembly 33 also includes a metal packing ring 71, anda metal packing retainer ring 73. Packing ring 71 lands on an upwardfacing annular shoulder 75 of body 13 formed within a stem opening 77that allows passage of stem 29 into cavity 21. Packing ring 71 includesan aligning annular surface 79 on an inner diameter of packing ring 71.Aligning surface 79 is conical and extends from a downward facingshoulder 81 of packing ring 71 into opening 77. Downward facing shoulder81 is adapted to land on annular shoulder 75 of body 13 so that packingring 71 will be coaxial with axis 25. Packing ring 71 includes a firstannular recess 83 formed on an outer diameter of packing ring 71proximate to annular shoulder 81. First annular recess 83 extends fromthe outer diameter of packing ring 71 inward to outwardly facingcylindrical surface 84 and from downward facing shoulder 81 to downwardfacing recess shoulder 85. First annular recess 83 will have a size andshape such that first seal 35A may be placed within first annular recess83. First seal 35A will substantially fill first annular recess 83 andbe positioned so that first end 49 (FIG. 3) of first seal 35A will abutupward facing shoulder 75 of body 13 (FIG. 2). Surface 69 of back ring43 of first seal 35A will be proximate to but optionally may not contactdownward facing recess shoulder 85. Preferably, distal end 59 of secondleg 55 seal ring 41 of first seal 35A will contact and seal to outwardfacing shoulder 84 of packing ring 71 within first annular recess 83.Similarly, distal end 57 of first leg 53 of seal ring 41 of first seal35A will contact and seal to a surface of body 13. Thus, first seal 35Awill seal against movement of fluid from cavity 21 to an exterior ofbody 13, and will vent fluid from an exterior of body 13 into cavity 21.

Packing ring 71 also defines a second annular recess 87 on a innerdiameter of packing ring 71. Second annular recess 87 extends from theinner diameter surface to land at a radially inward facing shoulder 89and from an upward facing shoulder 91 toward cavity 21 to land at anupward facing recess shoulder 93. Packing ring 71 also includes anannular portion 95 extending from an upper end of packing ring 71 near acenter of the width of packing ring 71 so that packing ring 71 definesupward facing shoulder 91 on an inner diameter side of annular portion95 and an upward facing shoulder 97 on an outer diameter side of annularportion 95. An load ring assembly 99 will be positioned on exteriorfacing shoulder 91 and extend upward a portion of the length of annularprotrusion 95. Load ring assembly 99 may comprise any suitable assemblyadapted to transfer load from second seal 35B to packing ring 71. In theillustrated embodiment, load ring assembly 99 does not transfer a loadapplied to second seal 35B to fourth seal 35D so that second seal 35Band fourth seal 35D operate independently of each other. In an exemplaryembodiment, load ring assembly 99 comprises a stem assembly similar to“Segmented Seal Ring and Support for Same” as disclosed in pending U.S.patent application Ser. No. 13/281,526, filed Oct. 26, 2011, andincorporated by reference in its entirety herein. A person skilled inthe art will recognize that other suitable annular stem assemblies maybe used provided that the stem assembly allows for independent loadingof second seal ring 35B and fourth seal ring 35D.

Second seal 35B will substantially fill second annular recess 87 and bepositioned so that first end 49 (FIG. 3) of second seal 35B will abutupward facing shoulder 93 of packing ring 71 (FIG. 2). Surface 69 ofback ring 43 of second seal 35B will be proximate to but may not contacta downward facing surface 101 of load ring assembly 99. Preferably,distal end 59 of second leg 55 of seal ring 41 of second seal 35B willcontact and seal to an outer diameter surface of stem 29. Similarly,distal end 57 of first leg 53 of seal ring 41 of second seal 35B willcontact and seal to inward facing shoulder 89 of second annular recess87 of packing ring 71. Thus, second seal 35B will seal against movementof fluid from cavity 21 to an exterior of body 13 along stem 29, andwill vent fluid into cavity 21 along stem 29 from an exterior of body13.

Packer retainer ring 73 includes an annular protrusion 103 extendingfrom a lower portion of packer retainer ring 73 towards cavity 21.Annular protrusion 103 has a width such that annular protrusion 103 willsubstantially fill a gap between annular protrusion 95 of packing ring71 and an inner diameter surface of opening 77. As illustrated, theouter diameter of annular protrusion 103 is flush with the outerdiameter of packing ring 71. Annular protrusion 103 will define a thirdannular recess 105 extending from the outer diameter of annularprotrusion 103 toward annular protrusion 95 to land at an outward facingshoulder 107. Third annular recess 105 will extend from an end ofannular protrusion 103 away from cavity 21 to land at a downward facingshoulder 109.

Third annular recess 105 will have a size and shape such that a thirdseal 35C may be placed within third annular recess 105. Third seal 35Cwill substantially fill third annular recess 105 and be positioned sothat first end 49 (FIG. 3) of third seal 35C will abut downward facingshoulder 109 of third annular recess 105 (FIG. 2). Surface 69 of backring 43 of third seal 35C will be proximate to but may not contactupward facing shoulder 91 of packing ring 71. Preferably, distal end 57of first leg 53 of seal ring 41 of third seal 35C will contact and sealto outward facing shoulder 107 within third annular recess 105.Similarly, distal end 59 of second leg 55 of seal ring 41 of third seal35C will contact and seal to a surface of body 13. Thus, third seal 35Cwill seal against movement of fluid from an exterior of body 13 tocavity 21, and will vent fluid from cavity 21 to an exterior of body 13.

Packer retainer ring 73 defines a downward facing shoulder 111 extendingfrom a base of annular protrusion 103 to an inner diameter of packerretainer ring 73 proximate to stem 29. Annular protrusion 95 of packingring 71 has a width that extends a portion of the width between annularprotrusion 103 of packer retainer ring 73 and the inner diameter ofpacker retaining ring 73 such that a fourth annular recess 113 existsbetween annular protrusion 95, downward facing shoulder 111 of packerretainer ring 73, and an upper surface 115 of load ring assembly 99.Fourth annular recess 113 extends from an area proximate to stem 29inward to inward facing surface 117 of annular protrusion 95.

Fourth annular recess 113 will have a size and shape such that a fourthseal 35D may be placed within fourth annular recess 113. Fourth seal 35Dwill substantially fill fourth annular recess 113 and be positioned sothat first end 49 (FIG. 3) of fourth seal 35D will abut upper surface115 of load ring, assembly 99 (FIG. 2). Surface 69 of back ring 43 offourth seal 35D will be proximate to but may not contact downward facingshoulder 111 of packer retaining ring 73. Preferably, distal end 57 offirst leg 53 of seal ring 41 of fourth seal 35D will contact and seal toinward facing surface 117 of annular protrusion 95 of packing ring 71within fourth annular recess 113. Similarly, distal end 59 of second leg55 of seal ring 41 of fourth seal 35D will contact and seal to a surfaceof stem 29. Thus, fourth seal 35D will seal against movement of fluidfrom cavity 21 to an exterior of body 13, and will vent fluid intocavity 21.

As illustrated in FIG. 2, second seal 35B and fourth seal 35D arepositioned so that the seals seal to stem 29 to prevent flow of fluidout of cavity 21 along stem 29 while allowing fluid that may leak pastsecond seal 35B to vent back into cavity 21. This provides a redundantsealing system that is more effective than prior art sealing methods.Similarly, the combined second and fourth seals 35B, 35D provide fluidventing that prevents damage to the seals where fluid pressure withincavity 21 is suddenly released. Similarly, first seal 35A and third seal35C are positioned to prevent fluid flow into cavity 21 along body 13.Unlike seals 35B and 35D, seals 35A and 35C do not provide redundantprotection. Instead, first and third seals 35A, 35C, respectively,provide opposite direction sealing. This potentially reduces the amountof fluid that may pass between an exterior of body 13 and cavity 21. Inaddition, first and third seals 35A, 35C, respectively, provide oppositedirection venting that protects both seals from damage in the event of asudden pressure change in the area sealed. A person skilled in the artwill understand that the sealing and venting directions of each seal,may be switched by flipping the position of each seal as needed.

Accordingly, the disclosed embodiments provide numerous advantages overthe prior art. For example, the disclosed embodiments provide aredundant sealing system that provides two independent and verifiableseals along the stem of the valve. This greatly improves effectivenessand reliability over prior art stem seals. In addition, the disclosedembodiments provide a venting mechanism to allow for release of fluidthat has leaked past the seals to vent in response to quick changes influid pressure within the valve cavity. This prevents damage to thefirst seal that may be caused by known leakage issues in all valvesealing mechanisms. In turn, this prolongs the life of the seal.

It is understood that the present invention may take many forms andembodiments. Accordingly, several variations may be made in theforegoing without departing from the spirit or scope of the invention.Having thus described the present invention by reference to certain ofits preferred embodiments, it is noted that the embodiments disclosedare illustrative rather than limiting in nature and that a wide range ofvariations, modifications, changes, and substitutions are contemplatedin the foregoing disclosure and, in some instances, some features of thepresent invention may be employed without a corresponding use of theother features. Many such variations and modifications may be consideredobvious and desirable by those skilled in the art based upon a review ofthe foregoing description of preferred embodiments. Accordingly, it isappropriate that the appended claims be construed broadly and in amanner consistent with the scope of the invention.

What is claimed is:
 1. A valve having a stem seal assembly comprising: avalve body defining a flow passage and a body cavity perpendicular tothe flow passage; the valve body further defining a stem openingextending from an exterior of the body into the body cavity; a valvemember moveable between an open position and a closed position, thevalve member blocking the flow passage in the closed position, andallowing flow through the flow passage in the open position; a valvestem having a valve stem axis coupled to the valve member, the valvestem extending from the body cavity to an exterior of the valve bodythrough the valve stem opening for moving the valve member from theclosed position to the open position; a spring energized first seal ringpositioned within the valve stem opening to seal the valve stem to thevalve body; a second seal ring positioned within the valve stem openingto seal the valve stem to the valve body; and a load ring assemblystationarily mounted to and defining a portion of the valve body betweenthe first seal ring and the second seal ring that isolates the firstseal ring and the second seal ring so that a force applied to the firstseal ring in a direction toward the second seal ring transfers to theload ring assembly.
 2. The valve of claim 1, wherein the first seal ringcomprises: a chevron profile defining a first and a second leg extendingfrom an apex of the chevron profile radially outward, the first andsecond legs sealing the stem and the body to opposing annular surfaces;and a back ring having a chevron channel that receives the apex of thechevron profile, the back ring having a greater stiffness to radialmovement than the first and second legs to limit radial deformation ofthe first and second legs.
 3. The valve of claim 2, wherein the firstseal ring further comprises: an annular seal stand off having a firstend and a second end; wherein a chevron profile is positioned on theseal standoff so that the second end of the seal stand off inserts intothe chevron profile; an energizing spring having a chevron profileinterposed between the seal stand off and the chevron profile, theenergizing spring exerting an expanding force on legs of the chevronprofile so that the chevron profile will remain in sealing contact withthe opposing annular surfaces; wherein the energizing spring may bedeflected in response to a fluid pressure on the chevron profileopposite the energizing spring to allow fluid flow past the chevronprofile; and wherein the first end of the seal stand off has asubstantially flat portion positioned on a supportive shoulder of thepacking assembly and the second end of the seal stand off is inoperative engagement with the chevron profile of the energizing spring.4. The valve of claim 2, wherein the chevron profile is formed of apolymer and the back ring is formed of a polymer having a greaterhardness than the polymer of the chevron profile.
 5. The valve of claim2, wherein the channel of the back ring extends only partially to distalends of each leg of the chevron profile.
 6. The valve of claim 2,wherein: a width of the back ring is smaller than a distance betweenouter side of distal ends of the seal ring legs; and an inner gap islocated between the back ring and the stem and an outer gap is locatedbetween the back ring and the body.
 7. The valve of claim 2, wherein thechannel of the back ring extends from the apex of the chevron profileover only part of the chevron profile.
 8. The valve of claim 2, wherein:the chevron profile has two exterior angled portions meeting at ajunction; and the angled portion from the apex to the junction has alarger angle relative to an axis passing through the apex than theangled portion from the junction to the distal ends of each seal ringleg.
 9. The valve of claim 2, further comprising a plurality of bumpscircumferentially spaced apart on the back ring, defining a plurality offluid channels, allowing fluid to vent past the surface of the chevronprofile.
 10. The valve of claim 1, wherein the first seal ring furthercomprises a bump formed on an outer surface of the first seal ringopposite an end of the seal ring that seals to the valve stem and thevalve body, the bump forming one or more fluid channels, allowing fluidto vent past the sealing surface of the seal ring.
 11. The valve ofclaim 1, wherein the second seal comprises a spring energized seal. 12.A valve stem packing assembly for sealing a valve stem to a valve bodyhaving a body cavity, the packing assembly comprising: a first springenergized seal ring positioned within a valve stem opening extendingaxially through the body to seal the valve stem to the valve body; asecond seal ring positioned within the valve stem opening to seal thevalve stem to the valve body; and a load ring assembly mounted to andforming a part of the body having a first end in engagement with thefirst seal ring and a second end in engagement with the second sealring, such that an axial force applied to the first seal ring transfersto load ring assembly, an axial force in an opposite direction on thesecond seal ring transfers to the load ring assembly.
 13. The packingassembly of claim 12, wherein the first seal comprises: an annular sealstand off having a first end and a second end; a seal ring having achevron profile positioned on the seal standoff so that the second endof the seal stand off inserts into the chevron profile; wherein the sealring defines a first and a second leg extending from an apex of thechevron profile radially outward, the first and second legs sealing toopposing annular surfaces of the stem and the body; an energizing springhaving a chevron profile interposed between the seal stand off and theseal ring, the energizing spring exerting an expanding force on legs ofthe seal ring so that the seal ring will remain in sealing contact withthe opposing annular surfaces; wherein the energizing spring may bedeflected in response to a fluid pressure on the seal ring opposite theenergizing spring to allow fluid flow past the seal ring; a back ringhaving a chevron channel that receives an apex of the seal ring, theback ring having a greater stiffness to radial movement than the firstand second legs of the seal ring to limit radial deformation of thefirst and second legs of the seal ring; and wherein the first end of theseal stand off has a substantially flat portion positioned on asupportive shoulder of the packing assembly and the second end of theseal stand off is in operative engagement with the chevron profile. 14.The valve of claim 13, further comprising a plurality of bumpscircumferentially spaced apart on the back ring, defining a plurality offluid channels, allowing fluid to vent past the sealing surface of theseal ring.
 15. The valve of claim 13, wherein the first seal ringfurther comprises a bump formed on an outer surface of the back ringopposite an end of the seal ring that seals to the valve stem and thevalve body, the bump forming one or more fluid channels so that fluidmay vent past the sealing surface of the first seal ring.
 16. The valveof claim 13, wherein: the seal ring is formed of a polymer; and the backring is formed of a polymer having a greater hardness than the polymerof the seal ring.
 17. The valve of claim 12, wherein the second sealring comprises a spring energized seal.
 18. A seal ring for a valve stemcomprising: an annular seal stand off having a first end and a secondend; a seal ring having a chevron profile positioned on the sealstandoff so that the second end of the seal stand off inserts into thechevron profile; wherein the seal ring defines a first and a second legextending from an apex of the chevron profile radially outward, thefirst and second legs sealing to opposing annular surfaces of the valvestem and a valve body; an energizing spring having a chevron profileinterposed between the seal stand off and the seal ring, the energizingspring exerting an expanding force on legs of the seal ring so that theseal ring will remain in sealing contact with the opposing annularsurfaces; wherein the energizing spring may be deflected in response toa fluid pressure on the seal ring opposite the energizing spring toallow fluid flow past the seal ring; a back ring having a chevronchannel that receives an apex of the seal ring, the back ring having agreater stiffness to radial movement than the first and second legs ofthe seal ring to limit radial deformation of the first and second legsof the seal ring; wherein the first end of the seal stand off has asubstantially flat portion positioned on a supportive shoulder of thepacking assembly and the second end of the seal stand off is inoperative engagement with the chevron profile; wherein the seal ring isformed of a polymer and the back ring is formed of a polymer having agreater hardness than the polymer of the seal ring; wherein the channelof the back ring extends only partially to distal ends of each leg ofthe seal ring; wherein a width of the back ring is smaller than adistance between outer sides of the distal ends of the seal ring legs;wherein an inner gap is located between the back ring and the stem andan outer gap is located between the back ring and the valve body;wherein the channel of the back ring extends from the apex of the sealring over only part of the seal ring; and a plurality ofcircumferentially spaced apart bumps formed on an outer surface of theback ring, defining a plurality of fluid channels so that fluid may ventpast the sealing surface of the seal ring.
 19. The valve of claim 18,wherein: the seal ring has two angled exterior portions meeting at ajunction; and the angled portion from the apex to the junction has alarger angle relative to an axis passing through the apex than theangled portion from the junction to the distal ends of each seal ringleg.